The present invention relates to stable polyisocyanate prepolymers containing hydroxy functions, a process for their manufacture, and their application to the manufacture of polyurethanes, in particular, foams having high hardness.
The reaction of an organic polyisocyanate with a mixture of polyols, in which the polyol mixture includes a polyol free from tertiary nitrogen and 5 to 40% by weight of a polyol containing a tertiary nitrogen and in which the polyol mixture has from 2 to 8 hydroxy groups and a molecular weight of 175 to 1,000, is already known from U.S. Pat. No. 3,468,819. One of ordinary skill in the art, however, has found that the resulting products of this reaction have both inadequate stability and high viscosities that complicate their use in the manufacture of polyurethanes.
Accordingly, there is a need for the development of polyisocyanate prepolymers containing hydroxy groups that do not separate and are simple to make, stable, and of acceptable viscosities that can be lowered further by dilution in a third polyol because of the stability of the product.